1. Field of the Invention
This invention generally relates to thin film mirrors, and more particularly, to a laminated film for thin film mirrors.
2. Discussion of the Related Art
Glass mirrors have been used for centuries and characteristically include a piece of glass as the substrate carrier for supporting a reflective metal coating. There are generally two types of glass mirrors, e.g. medicine cabinet mirrors and optical mirrors. Medicine cabinet mirrors are the most common type of glass mirrors and are considered xe2x80x9csecond-surfacexe2x80x9d mirrors in that they comprise a metal surface, one side of which is covered by a piece of glass and the other side of which may be covered with a protective coating. When looking through the glass the reflection is seen on the metal surface beneath the glass. The second type of glass mirrors are optical mirrors, which are considered xe2x80x9cfirst-surfacexe2x80x9d mirrors because the reflective metal is applied directly to the surface of the piece of glass that serves only as a substrate carrier for the metal. The reflection is observed directly on the face of the metal, which is typically protected by a protective coating such as silicone oxide.
Relatively small size glass mirrors are efficient and cost effective, however, in larger size mirrors, as for example, 24 inchesxc3x9736 inches and greater, the increased weight, potential for breakage, and difficulty in realizing a desired substantially planar surface for optical purposes results in mechanical and safety problems.
Thin film mirrors have been developed to overcome the disadvantages associated with glass mirrors. These mirrors are particularly advantageous as a substitute for relatively large glass mirrors because of their relative light weight and structural stability (substantially flat surface).
The film used to manufacture thin film mirrors is typically a transparent polyester film, such as polyethylene terephthalate, having a bi-axially oriented thermal shrinkage, that is, the film undergoes thermal shrinkage in both the machine (longitudinal) direction of the film and in the transverse (lateral) direction of the film. A reflective metal layer is applied to one side of the film and a coating may be applied to the exposed surface of the reflective metal to protect it from corrosion and rough handling. U.S. Pat. No. 4,666,263 describes an alternative method of protecting the reflective metal by adding other metals to it. When the thin film mirror is used in a benign environment, the reflective metal may be left exposed.
Generally the thickness of the polyester film is between approximately 0.001 inch (25 microns) and approximately 0.002 inch (50 microns). Thinner films are advantageous in that they exhibit enhanced reflectivity, contrast, and resolution, but are fragile and awkward to handle during manufacture.
It is therefore desirable to provide a laminated film for use in thin film mirrors that solves the aforementioned problems associated with thinner films.
It is an object of the present invention to provide a laminated film for a thin film mirror in which light rays pass through a thinner polyester film than conventional films thereby producing a sharper, brighter, and higher contrast image.
It is a further object of the invention to provide a laminated film for a thin film mirror which retains the handling characteristics and strength associated with films of conventional thickness.
In accordance with the above-mentioned and other objects, a laminated film is provided for a thin film mirror. The inventive laminated film includes a transparent first polyester film, a first reflective metal layer deposited on one surface of the first polyester film, a laminating adhesive covering at least a portion of the first reflective layer, and a second polyester film affixed to the first reflective metal layer by the laminating adhesive. The thickness of the first polyester film is substantially equal to the thickness of the second polyester film. In addition, the first and second polyester films each have a thermal shrinkage and a thickness less than or equal to approximately 0.001 inch. Together the total thickness of the first and second polyester films is less than or equal to approximately 0.002 inch. In an alternative embodiment the arrangement of the first reflective metal layer and laminating adhesive may be interchanged.
The invention also relates to a process for forming a laminated film for the thin film mirror as described above. Initially, a reflective metal is deposited on one surface of a transparent first polyester film having a thermal shrinkage and a thickness less than or equal to approximately 0.001 inch. The reflective metal deposited on the first polyester film is then affixed to a second polyester film having a thermal shrinkage and a thickness less than or equal to approximately 0.001 inch using a laminating adhesive. The thickness of the first polyester film is substantially equal to the thickness of the second polyester film, and a total thickness of the first and second polyester films is less than or equal to approximately 0.002 inch. In an alternative process in accordance with the present invention, the reflective metal may be deposited on one surface of a first polyester film having a thermal shrinkage and a thickness less than or equal to approximately 0.001 inch. The reflective metal deposited on the first polyester film is then affixed to a second transparent polyester film having a thermal shrinkage and a thickness less than or equal to approximately 0.001 inch using a laminating adhesive. The thickness of the first polyester film is substantially equal to the thickness of the second polyester film, and a total thickness of the first and second polyester films is less than or equal to approximately 0.002 inch.
In addition the present invention is directed to a laminated film for a thin film mirror including a transparent first polyester film, a first reflective metal layer deposited on one surface of the first polyester film, a second polyester film, a second reflective metal layer deposited on one surface of the second polyester film, and a laminating adhesive interposed between the first and second reflective metal layers. The thickness of the first polyester film is substantially equal to the thickness of the second polyester film. In addition, the first and second polyester films each have a thermal shrinkage and a thickness less than or equal to approximately 0.001 inch. Together the thickness of the first and second polyester films is less than of equal to approximately 0.002 inch.
The invention also relates to a process for manufacturing the laminated film for a thin film mirror. Initially, a first reflective metal is deposited on one surface of a transparent first polyester film having a thermal shrinkage and a thickness less than or equal to approximately 0.001 inch and a second reflective metal is deposited on one surface of a second polyester film having a thermal shrinkage and a thickness less than or equal to approximately 0.001 inch. Then, the first and second polyester films are affixed together so that the first reflective metal is in intimate contact with the second reflective metal. The first and second polyester films are selected so that their respective thicknesses are substantially equal and the total thickness of the two polyester films is less than or equal to approximately 0.002 inch.
Furthermore, the present invention is directed to the laminated film and process for manufacturing the laminated film as described above, except that instead of using polyester films each having a thickness less than or equal to approximately 0.001 inch, the only constraint used to select the films is that the total combined thickness of the first and second polyester films be less than or equal to approximately 0.004 inch.